This is where battery packs can come in handy, but even then battery packs are limited in their capacity, at least until Anker came along and unveiled their upcoming Power House battery pack. This is a battery pack that features a 434Wh battery under the hood. It is also pretty big which means that it is obviously not meant to be carried with you everywhere on a daily basis.
It will probably come in handy if you are travelling to countries or areas where running electricity isn’t reliable or readily available, or if you are planning on camping out for a week or two. The Power House is said to be able to charge a smartphone 40 times before being depleted. Alternatively it can also charge laptops, mini fridges, or even power a 15V light bulb for more than 100 hours.